The present invention relates to a short range ultrasonic distance warning system in a motor vehicle having a rear-end transmitter and receiver arrangement, a front-end transmitter and receiver arrangement having at least one transmitter and receiver unit for a central front area of the vehicle and one transmitter and receiver unit for front corner areas of the vehicle, a controller for activating and deactivating the transmitter and receiver arrangements and at least one of acoustic and optical warning elements which, when the transmitter and receiver arrangements are activated, are operatively associated therewith to generate warning signals as a function of the output signals thereof. In such a warning system a transmitter and receiver arrangement are at the rear end and at the front end, and operate with ultrasound for the detection of nearby objects at a distance of typically up to one or a few meters. Differing from longer range distance warning systems, such as are used for controlling the safety spacing during the journey, a short range warning system of this type is predominantly used as a parking aid which is intended to support the driver in the estimation of distances from objects in invisible vehicle areas.
U.S. Pat. No. 5,173,881 discloses a known ultrasonic distance warning system where, apart from in each case a longer range transmitter and receiver unit at the front and at the rear, short range transmitter and receiver arrangements are positioned in the four vehicle corner areas and in each case therebetween at the front, at the rear and on the sides. Each arrangement consists of a pair of transmitter and receiver units with a lateral emission angle of about 120.degree.. As a warning indicator, a warning element is provided which, as a function of the position and distance of a detected object relative to the vehicle, provides optical indications in graduated colors and, in the case of a very short distance, an acoustic indication as well. The activation and deactivation of the distance warning system is carried out as a whole at the driver's request, for example by a dedicated remote control, together with the actuation of the ignition or a door locking system or by actuating the gears.
In an article entitled "Ultraschallechos als Parkpilot" [translation, Ultrasonic Echoes As Parking Guide] in the "Radio Fernsehen Elektronik" [translation, Radio, TV, Electronics], Vol. 10, p. 594, an ultrasonic distance warning system is described for monitoring the rear vehicle area as a parking aid. This system includes positioning up to eight sensors and being automatically activated by selecting reverse gear. The warning indication is carried out optically in different colors, graduated according to distance, and in the case of a very short distance by an acoustic signal as well.
In Laid-Open Application JP 60/152968, an ultrasonic distance warning system is described in which, inter alia, two short range and a long range transmitter and receiver unit are arranged in each case at the front and at the rear. The activation of the various units is carried out such that in the case of a low speed in the forward direction, the front-end, short range units are activated, whereas in the case of a low speed in the reverse direction the rear-end, short range units are activated and at high speed the two long range units are activated.
Laid-Open Application DE 38 13 083 A1 discloses an automatic parking device for motor vehicles which, to measure distance, uses ultrasonic distance measuring units of which one in each case is arranged emitting laterally and one to the front or to the rear at each vehicle corner area. The ultrasonic distance measuring units are controlled by a microcomputer so that only the measuring units emitting to the left or to the right laterally are actuated when the vehicle is travelling forwards, in order to look for a parking position on the left-hand or right-hand side. The measuring units arranged on the right-hand vehicle side are actuated when the vehicle is travelling backwards in order to park on the right-hand side parallel to the roadway, and only the two measuring units emitting to the rear are actuated when the vehicle is travelling backwards in order to park on the right-hand side at right angles to the roadway.
Laid-Open Application DE 42 08 065 A1 describes a distance warning device which has light-optical transmitter/receiver units which are arranged in the vehicle corner areas and are switched on with the selection of reverse gear and/or a low forward gear.
German Patent Specification 32 44 358 C2 describes a device for the detection of obstacles as a maneuvering aid during parking or turning a motor vehicle. Optical indicator elements and/or an acoustic indicator device can be provided to generate sound pulses which vary with respect to pitch and/or repetition frequency with the distance of an obstacle from the vehicle. Provision can also be made for the maneuvering aid device to be switched on automatically as a result of the selection of reverse gear, if appropriate in combination with releasing the handbrake and/or releasing the clutch pedal or beginning a backwards movement of the vehicle.
It is an object of the present invention to provide a short range ultrasonic distance warning system, suitable as a parking aid which makes possible the optimum detection of, for example, objects occurring in the vicinity of the vehicle during a parking process, and operates without unnecessary system activation.
This object has been achieved in accordance with the present invention by a short range ultrasonic distance warning system in which both the front-end and the rear-end transmitter and receiver arrangements are operatively configured to be activated when a reverse gear is active and speed of travel of the vehicle has not exceeded a prescribed first deactivation limiting value, only the front-end transmitter and receiver arrangement is activated when reverse gear is not active and the speed of travel has not exceeded a prescribed second deactivation limiting value, and both transmitter and receiver arrangements are deactivated during all other driving conditions.
In this arrangement, in a manner which saves power and avoids unnecessary ultrasonic emissions, the system parts in each case are kept activated, that is to say operationally ready, only when this can also lead to practical detection results. Thus, the entire system is kept inactive if the vehicle speed exceeds prescribed threshold values, since there is no parking process at speeds of this type and, above all, an object detection within the prescribed short range of at most one to a few meters could no longer be put to profitable use.
Also, when reverse gear is not being selected, the rear-end system part is kept inactive, because it is not needed during periods of forward travel. In contrast, in the case of periods of reverse travel, both the front-end and the rear-end system part are kept active to enable objects in the rear space and also such in the lateral front space to be detected, for optimum object registration. The latter is in particular effected by the front laterally arranged transmitter and receiver units. This is advantageous because just in the front corner regions during backward parking, as a result of applying severe lock to the steering, a collision-threatening approach to an already parked vehicle can be produced, which is often not detected until it is too late by the driver who, in this situation, is predominantly directing his attention to the rear space.
A further feature of the present invention results in a response hysteresis with respect to the activation and deactivation of the system, thereby preventing undesirably frequent switch-overs between the system states in the case of travel speeds in the vicinity of the switch-over threshold range.
An advantageous embodiment of the present invention provides warning elements having integrated optical and acoustic warning functions. One such element is assigned to the backward and two other elements are assigned to the front-end monitoring area. In a further contemplated embodiment, each warning element has an optical bar graph indicator with yellow and red fields which light up increasingly in a graduated manner as the distance from a detected object decreases, as well as an acoustic indicator which, in an advantageous manner, is driven such that the relationships during a parking process are particularly taken into account. For this purpose, in particular, loudspeaker activation is used in the case of forward travel only at a very small distance from an obstacle in the front corner areas, in order, for example, not to disturb unparking. Loudspeaker activation is used in the case of backward travel already at comparatively large distances from obstacles in the front-end monitoring area, in order that the driver who is looking to the rear can perceive a front-end approach to an obstacle in good time.